The present and foregoing application claim priority to Japanese Application No. P2000-176215 filed Jun. 13, 2000. All of the foregoing applications are incorporated herein by reference to the extent permitted by law.
The present invention relates to a display apparatus, and particularly to a display apparatus suitable for an active matrix type organic electroluminescence display using an organic electroluminescence device as a display device.
An organic electroluminescence device utilizing electroluminescence (hereinafter referred to as xe2x80x9cELxe2x80x9d) of an organic material comprises an organic layer in which an organic positive hole transport layer and an organic luminescence layer are laminated between an anode and a cathode, and is paid attention to as a light emitting device capable of high luminance light emission by a low voltage DC driving.
Of display apparatuses using such an organic EL device as a display device, an active matrix type display apparatus comprising a thin film transistor (hereinafter referred to as xe2x80x9cTFTxe2x80x9d) for driving an organic EL device at each pixel comprises a flattening insulation film in the condition of covering the TFT and a wiring provided on a substrate, and the organic EL device is provided on the flattening insulation film. The organic EL device and the wiring are connected to each other through a contact hole provided in the flattening insulation film.
As the flattening insulation film, as disclosed, for example, in Japanese Patent Laid-open No. Hei 10(1998)-189252, there have been used a film provided by spin coating of a resin material such as a polyimide, and a film produced by building up a silicon oxide-based material film or a silicon nitride-based material film by CVD (Chemical Vapor Deposition), followed by polymer coating and etching back the entire surface by RIE (Reactive Ion Etching).
However, these display apparatuses have the following problems.
Namely, the flattening insulation film formed by coating such as spin coating consists mostly of an organic material or contains an organic material, and, therefore, has a high water-absorbing property. For example, a polyimide film formed by coating using a commercially available coating liquid has a water absorption coefficient as high as about 1 to 3%. Since the organic EL device used as a display device has a light-emitting portion composed of an organic material, absorption of moisture would result in lowering of luminance or a rise of driving voltage. Therefore, where a material high in moisture absorption property as above is used as a flattening insulation film, moisture gradually released from the flattening insulation film has a heavy effect on the display performance of the display device, and, therefore, sufficient long-term reliability as display apparatus cannot be obtained. In addition, since the deterioration of the display device due to moisture absorption proceeds also in the process of producing the display apparatus, the release of moisture from the flattening insulation film causes lowering of the yield of the display apparatus.
On the other hand, in the case of formation of the flattening insulation film by CVD method and etching back using RIE, it is difficult to obtain a flatness sufficient for the organic EL device provided later on the flattening insulation film. Particularly, in the case of etching back the entire surface by RIE, weak portions of the film to be etched are etched selectively. Therefore, although large recesses and projections formed by embedding a wiring or the like are alleviated, etching of an initial surface of the film to be etched which is not perfectly flat proceeds so that the grain shape of the film being etched is exaggerated, and the flatness of the etched-back film is further damaged. In addition, where a substrate with a large area is used, it is very difficult to obtain a uniform flatness over the entire surface of the substrate.
Where a display device is provided on the flattening insulation film having such an insufficient flatness, it is difficult to obtain a uniform film thickness of each layer constituting the display device, and it is difficult to obtain uniform display characteristics. Particularly, since a light-emitting portion of the organic EL device used as the display device is composed of an extremely thin organic film, dispersion of film thickness would affect the display characteristics. For example, there would arise troubles such as leakage of current due to local concentration of electric field at a small film thickness portion at the time of driving, and it is difficult to accomplish stable display.
Accordingly, it is an object of the present invention to solve the above-mentioned problems and to provide a display apparatus suitable for an active matrix type display apparatus excellent in yield and long-term reliability.
According to the present invention, there is provided a display apparatus including an interlayer insulation film provided on a substrate in the condition of covering recesses and projections of the substrate, and a display device provided on the interlayer insulation film, wherein the interlayer insulation film includes a flattening insulation layer made from an organic compound-containing material and formed in the condition of embedding the recesses and projections, and a coat layer consisting of an inorganic material and formed in the condition of covering the surface of the flattening insulation layer.
With this configuration, since the flattening insulation layer is constituted of an organic compound-containing material, the flattening insulation layer can be provided as a coat film having excellent flatness. Therefore, the flattening insulation layer together with the coat layer provides an interlayer insulation film excellent in flatness, and the display device can be provided on the interlayer insulation film, so that the film thickness of each layer constituting the display device is made to be uniform. In addition, since the coat layer is composed of an inorganic material, the coat layer functions as a barrier against gas components (for example, water vapor) released from the organic material constituting the flattening insulation layer, and supply of the gas components (particularly, water vapor) to the side of the display device provided on the coat layer is prevented, whereby deterioration of the display device due to moisture absorption is prevented.
Thus, as detailed below, according to the display apparatus of the present invention, the display device is provided on an interlayer insulation film having a multiplayer structure comprising a flattening insulation layer and a coat layer, whereby it is possible to stabilize the display characteristics of the display device provided through the interlayer insulation film on a substrate having recesses and projections due to a wiring such as, for example, a substrate of an active matrix type display apparatus, and it is possible to prevent deterioration due to moisture absorption. Therefore, it is possible to contrive a higher yield and a higher long-term reliability of the display apparatus.
The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings which show by way of example some preferred embodiments of the invention.